Optical encoder device

ABSTRACT

An optical encoder device ( 100 ) comprises: an optical emitter ( 103 ) for emitting light, the optical emitter ( 103 ) having a light emission direction (E); an optical detector ( 104 ) for detecting light emitted by the optical emitter ( 103 ), the optical detector ( 104 ) having a light detection direction (D) which is different from the light emission direction (E); an optical element ( 109 ) for controlling an optical path ( 108 ) between the optical emitter ( 103 ) and the optical detector ( 104 ) such that light emitted by the optical emitter ( 103 ) can be detected by the optical detector ( 104 ); and a free area ( 113 ) in the optical encoder device ( 100 ) for accommodating a moveable optical encoding unit ( 112 ) comprising a plurality of alternating transparent and opaque encoding elements such that the plurality of alternating transparent and opaque encoding elements of the optical encoding unit ( 112 ) is able to affect the optical path ( 108 ).

BACKGROUND AND RELATED ART

[0001] The present invention relates to an optical encoder device, andmore specifically to the detailed design of an optical encoder device.

[0002] An encoder is a device that provides feedback to a closed loopsystem. The encoder enables a signal interpretation such as to obtaininformation on a position, velocity, acceleration and/or the like whenthe encoder works in conjunction with a codewheel or a codestrip.Codewheels are generally used for detecting the rotational motion, forexample of a paper feeder drum in a printer or a copying machine, whilecodestrips are used for detecting the linear motion, for example of aprint head of a printer.

[0003] Usually, the motion of the codewheel or the codestrip is detectedoptically by means of an optical emitter and an optical detector.Therefore, the encoder is usually an optical encoder. The opticalemitter emits light in a light emission direction towards thecodewheel/codestrip. The codewheel/codestrip comprises a regular patternof slots and bars. According to the position of the slots and barsrelative to the light emission direction, the codewheel/codestripalternately permits and prevents light passing therethrough. The opticaldetector is positioned behind the codewheel/codestrip, when seen in thedirection of the light emission from the optical emitter, and detects alight signal based on the light emitted by the optical emitter andtransmitted through the codewheel/codestrip. The detected light signalis either quadruple or sinusoidal and the frequency of said light signalyields an unambiguous information on the motion of thecodewheel/codestrip.

[0004] Due to the special arrangement of the optical emitter and theoptical detector of such an optical encoder, the optical encoder housingfor accommodating the optical encoder is generally C-shaped. The opticalencoder together with the C-shaped optical encoder housing form aC-shaped optical encoder device. The codewheel/codestrip is passedthrough the free area (the recess) of the C-shaped optical encoderdevice and moves such that the optical encoder can detect the slots andbars formed in the codewheel/codestrip. FIG. 2A and FIG. 2C showcross-sections through and FIG. 2B and FIG. 2D show top views of such aC-shaped optical encoder device 201 together with a codewheel 202 and acodestrip 203, respectively. The codewheel 202 and the codestrip 203 areprovided with a regular pattern of slots 204 (and bars between the slots204) which are arranged such that a motion of the codewheel 202 or thecodestrip 203, respectively, is unambiguously detectable. Therefore, thecodewheel 202 or the codestrip 203, respectively, is passed through thefree area 205 of the generally C-shaped optical encoder device 201 whichtakes up the codewheel 202 or the codestrip 203, respectively. If thecodewheel 202 is rotated around the center axis C in a directionindicated by the arrows 206, or if the codestrip 203 is linearly movedin a direction indicated by the arrows 207, respectively, the slots 204(and the bars between the slots 204) cause an alternating light signalin the optical detector of the optical encoder which results in anunambiguous information on the motion of the codewheel 202 or thecodestrip 203, respectively.

[0005] Generally, the C-shaped optical encoder device 201 is mounted ona printed circuit board (PCB) which is positioned inside the appliance,e.g. a printer or a copying machine, and which is used for an electricalcoupling of the optical encoder to the control unit of the appliance.The C-shaped optical encoder device 201 itself comprises as maincomponents an optical emitter 208 and an optical detector 209. Theoptical emitter 208 may be a light emitting diode, whereas the opticaldetector 209 is usually an array of photodiodes. The optical emitter 208and the optical detector 209 are arranged inside the C-shaped opticalencoder device 201 such that a straight optical path 211 results forlight, which is emitted by the optical emitter 208 and detected by theoptical detector 209. Light, which is emitted by the optical emitter 208and travels along the optical path 211, is first collimated intoparallel light by means of an optical lens 210, which is positioned nextto the optical emitter 208, then transmitted through the free area 205and partly through the codewheel 202 or the codestrip 203, respectively,and finally detected by the optical detector 209, which is placedopposite to the optical emitter 208. Due to the opposite arrangement ofthe optical emitter 209 and the optical detector 209 relative to thecodewheel 202 or the codestrip 203, respectively, a special opticalthrough-beam solution for the codewheel 202 or the codestrip 203,respectively, is provided. This optical through-beam solution provides agood performance for detecting the motion of the codewheel 202 or thecodestrip 203, respectively.

[0006] However, the available optical encoder devices according to theprior art are manufactured with a large number of piece parts inlarge-scale processes and with extensive production costs.

[0007]FIG. 3A shows a cross-section through a first type of opticalencoder device 301 according to the prior art. The first optical encoderdevice 301 comprises an optical emitter 208 and an optical detector 209which are arranged on a lead frame 302. The lead frame 302 is buried ina housing material 304 and comprises an electrical circuitry (notshown), which is used for electrically contacting the optical emitter208 and the optical detector 209. Generally, the optical emitter 208 andthe optical detector 209 are each covered with a capsule 303. Duringmanufacturing the optical encoder device 301 the optical emitter 208 andthe optical detector 209 are first placed on a single common flat leadframe 302 and then covered with the capsules 303. Afterwards, the flatcommon lead frame 302 with the optical emitter 208, the optical detector209 and the capsules 303 is covered with an optical transparent housingmaterial 304. Further, an optical lens 210 is provided directly abovethe optical emitter 208 and partly inside the housing material 304.Additionally, a window 305 is provided directly above the opticaldetector 209 and partly inside the housing material 304.

[0008] The optical lens 210 and the window 305 are provided to enable asatisfying optical transmission for light through the surface of thehousing material 304 at predetermined places. Further, the optical lens210 is provided to collimate light, which is emitted by the opticalemitter 208, into parallel light beams. After manufacturing the opticallens 210 and the window 305 the intermediate device is divided in anoptical emitter element 306 and an optical detector element 307. Then,the optical emitter element 306 is placed above the optical detectorelement 307, as indicated with arrow 308 in FIG. 3A, such that theoptical emitter 208 together with the optical lens 210 is placedopposite to the optical detector 209 and the window 305 for forming aC-shaped optical encoder. Finally, the optical emitter element 306 isfixed to the optical detector element 307 with a mounting bracket (notshown). Therefore, light emitted by the optical emitter 208 iscollimated by the optical lens 210, transmitted through the free area205 between the optical emitter 208 and the optical detector 209 andthrough the window 305 and detected by the optical detector 209. Thus,the first type of optical encoder device 301 represents a folded devicecomprising the optical emitter element 306 and the optical detectorelement 307.

[0009]FIG. 3B shows a cross-section through a second type of opticalencoder device 310 according to the prior art. In contrast to the firsttype of optical encoder device 301 described above, the second type ofoptical encoder device 310 is manufactured differently and comprises aC-shaped encoder housing 311 with a free area (recess) 205. The encoderhousing 311 comprises optical transparent material and an optical lens210. An optical emitter element 312 and an optical detector element 313are separately manufactured and subsequently inserted into respectiverecesses formed in the encoder housing 311 such that the optical emitter208 is placed next to the optical lens 210. The optical emitter element312 and the optical detector element 313 each comprise a lead frame 314,on which the optical emitter 208 and the optical detector 209,respectively, are mounted as well as a housing. The lead frames 314comprise an electrical circuitry (not shown) for electrically contactingthe optical emitter 208 and the optical detector 209, respectively.Therefore, this second type of optical encoder device 310 represents acomposed device with individually manufactured elements.

[0010] However, the first type of optical encoder device 301 and thesecond type of optical encoder device 310 according to the prior arthave some disadvantages. Among others, they need a large number of pieceparts and involve large-scale processing methods and, thereby, causehigh production costs.

[0011] Therefore, it is an object of the present invention to overcomesome or all disadvantages of the prior art.

SUMMARY OF INVENTION

[0012] An optical encoder device according to a main aspect of thepresent invention comprises: an optical emitter for emitting light, theoptical emitter having a light emission direction; an optical detectorfor detecting light emitted by the optical emitter, the optical detectorhaving a light detection direction which is different from the lightemission direction; an optical element for controlling an optical pathbetween the optical emitter and the optical detector such that lightemitted by the optical emitter can be detected by the optical detector;and a free area in the optical encoder device for accommodating amoveable optical encoding unit comprising a plurality of alternatingtransparent and opaque encoding elements such that the plurality ofalternating transparent and opaque encoding elements of the opticalencoding unit is able to affect the optical path.

[0013] Light in the context of the present invention can beelectromagnetic radiation of any wavelength, particularly visible light,ultraviolet radiation and/or infrared radiation, for instance.

[0014] One advantage of the present invention over the prior art is thatthe optical encoder device according to the present invention enablesboth an optical through-beam solution for the optical encoding elementsuch as a codewheel/codestrip and a single unfolded common substratecomprising both the optical emitter and the optical detector. Theoptical through-beam solution for the optical encoding element has theadvantage of a high performance and the single unfolded common substratehas the advantage that the optical encoder device according to thepresent invention can be manufactured with simple manufacturingoperations and with few process steps. Another advantage of the presentinvention is that the number of piece parts, which have to be alignedand fixed to each other, is reduced with respect to the prior art. Afurther advantage of the present invention is that by means of thesimplified manufacturing operations, the reduced process steps and thereduced number of piece parts the product costs are reduced.

[0015] The above and other objects, features and advantages of thepresent invention will become apparent from the following descriptionand the appended claims, taken in conjunction with the accompanyingdrawings in which like parts or elements are denoted by like referencenumbers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows a cross-section through an optical encoder deviceaccording to a first preferred embodiment of the present invention;

[0017]FIGS. 2A and 2C show cross-sections through a schematic opticalencoder device according to the prior art;

[0018]FIGS. 2B and 2D show top views of a schematic optical encoderdevice according to the prior art;

[0019]FIG. 3A shows a cross-section through a first type of opticalencoder device according to the prior art;

[0020]FIG. 3B shows a cross-section through a second type of opticalencoder device according to the prior art;

[0021]FIG. 4 shows a cross-section through an optical encoder deviceaccording to a second preferred embodiment of the present invention;

[0022]FIG. 5 shows a cross-section through an optical encoder deviceaccording to a third preferred embodiment of the present invention; and

[0023]FIG. 6 shows a cross-section through an optical encoder deviceaccording to a fourth preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Preferred embodiments of the present invention will now bedescribed with reference to the accompanying drawings in which likeparts or elements are denoted by like reference numbers.

[0025]FIG. 1 shows a cross-section through an optical encoder device 100according to a first preferred embodiment of the present invention.

[0026] The optical encoder device 100 is substantially C-shaped andcomprises a substrate 101 having an electrical circuitry 102, an opticalemitter 103, an optical detector 104 and an optical element 109. Theoptical emitter 103 and the optical detector 104 are electricallyconnected to the electrical circuitry 102, are mounted adjacent to eachother on a flat inward surface S of the substrate 101 and each of themis covered with a capsule 105. In general, according to the invention,the substrate 101 can be e.g. a lead frame, an insert-molded lead frame,a printed circuit board (PCB), a ceramics substrate or amicrointerconneting device (MID). In this embodiment of the invention,the optical encoder device 100 is described in connection with aninsert-molded lead frame as the substrate 101. The optical emitter 103has a light emission direction which is indicated with reference sign E.The optical detector 104 has a light detection direction which isindicated with reference sign D and which is different from the lightemission direction E of the light emitter 103. According to the firstpreferred embodiment of the present invention, the optical emitter 103and the optical detector 104 are arranged such that the light emissiondirection E and the light detection direction D are at leastsubstantially antiparallel. The lead frame 101 encloses an air gap 106and comprises an optical lens 107 above the optical emitter 103substantially in light emission direction E. The optical lens 107 can beattached to the lead frame 101. Light, which is emitted by the opticalemitter 103, is collimated by the optical lens 107 into parallel lightbeams and enters the optical element 109 in light emission direction Eabove the light emitter 103 as well as above the light detector 104. Thelight, which is emitted by the optical emitter 103 and enters theoptical element 109, travels along an optical path 108 inside theoptical element 109 towards the optical detector 104.

[0027] According to the present invention, the optical element 109 isarranged such that it allows internal reflection inside the opticalelement 109. Therefore, the optical element 109 comprises opticaltransparent material as well as a flat first surface 110 and a flatsecond surface 111 facing each other. The first surface 110 and thesecond surface 111 are arranged in the optical element 109 opposite tothe light emitter 103 and the light detector 104, and interface theadjacent medium next to the optical element 109.

[0028] If light encounters from a high-density medium an interfacebetween the high-density medium and a low-density medium, the light isgenerally refracted away from the normal plane of the interface (Snell'sLaw). If the angle enclosed between the direction of the encounteringlight and the normal plane of the interface is larger than a criticalvalue, the light is totally reflected at the interface and does notleave the high-density medium. This behavior is known as total internalreflection. The first surface 110 and the second surface 111 eachenclose a predetermined angle with the light emission direction E suchthat the predetermined angles are larger than the critical angle of theinterfaces between the optical element 109 and the adjacent medium.According to the present invention, the optical element 109 comprises anepoxy resin, whereas the adjacent medium is air. Therefore, the criticalangle for the first surface 110 and the second surface 111 is around41°. Thus, the first surface 110 and the second surface 111 control theoptical path 108 between the optical emitter 103 and the opticaldetector 104.

[0029] To ensure a complete reflection of the encountering light at thefirst surface 110 and the second surface 111, the optical element 109may be coated with reflective material on the first surface 110 and/orthe second surface 111. Such a coating is useful to make the opticalelement 109 less susceptible to manufacturing inaccuracies of theoptical encoder device 100 or fluctuations of the light emissiondirection E during the operation of the light emitter 103 and,therefore, prevents an undesired light loss at the first surface 110 andthe second surface 111, respectively.

[0030] According to the first preferred embodiment of the presentinvention, the first surface 110 encloses a first angle of at leastsubstantially −45° with respect to the light emission direction E of thelight emitter 103, whereas the second surface 111 encloses a secondangle of at least substantially +45° with respect to the light emissiondirection E of the light emitter 103. The light, which enters theoptical element 109 above the optical emitter 103 and travels along theoptical path 108, encounters the first surface 110, is totally reflectedat the first surface 110 and directed towards the second surface 111.After travelling to the second surface 111, this light is totallyreflected at the second surface 111 such that it is now directed to theoptical detector 104. Therefore, due to the first surface 110 and thesecond surface 111, the optical path 108 is substantially U-shaped.

[0031] According to the present invention, the optical emitter 103 is alight emitting diode and the optical detector 104 comprises an array ofphotodiodes. The optical emitter 103 may emit light as a point source,as a slit source, as a plane source or as a volumetric source. Theoptical encoder device 100 further comprises a free area 113 foraccommodating a moveable optical encoding unit 112 comprising aplurality of alternating transparent and opaque encoding elements.According to the present invention, the optical encoding unit 112 is acodewheel/codestrip and comprises a regular pattern of slots and bars(not shown). The optical encoding unit 112 is arranged such that theregular pattern is able to affect the optical path 108. A signalprocessor (not shown) is electrically connected to the optical detector104 for processing the electrical signals generated by the opticaldetector 104 on the basis of a variation of detected light, which iscaused by a movement of the optical encoding unit 112 inside the freearea 113. According to the first preferred embodiment of the presentinvention, the free area 113 is arranged inside the optical element 109between the first surface 110 and the second surface 111.

[0032] The optical element 109 is integrally formed and, therefore, themanufacturing of the optical encoder device 100 involves a less numberof product parts compared to the prior art.

[0033]FIG. 4 shows a cross-section through an optical encoder device 400according to a second preferred embodiment of the present invention.Parts already known from FIG. 1 will not be described again.

[0034] The only difference between the optical encoder device 400according to the second preferred embodiment of the present inventionand the optical encoder device 100 according to the first preferredembodiment of the present invention is that the free area 113 isarranged inside the optical element 109 between the second surface 111and the optical detector 104. The fact that the free area 113 ispositioned closer to the optical detector 104 has the advantages thatoptical diffractions caused by the optical encoding unit 112 arereduced, since the residual optical path 108 between the opticalencoding unit 112 and the optical detector 104 is short, and that theresponse time to a movement of the optical encoding unit 112 is reduced.

[0035]FIG. 5 shows a cross-section through an optical encoder device 500according to a third preferred embodiment of the present invention.Parts already known from FIG. 1 or FIG. 4 will not be described again.

[0036] In contrast to the optical encoder devices 100 and 400 accordingto the first and second preferred embodiments of the present invention,the optical encoder device 500 according to the third preferredembodiment of the present invention comprises a substrate 501, which isburied in the optical element 109 opposite of a non-flat first surface502 and the flat second surface 111. As in the first and secondpreferred embodiments of the invention, the substrate 501 can be e.g. alead frame, an insert-molded lead frame, a printed circuit board (PCB),a ceramics substrate or a microinterconneting device (MID). The presentembodiment will be described in conjunction with an insert-molded leadframe as substrate 501. The insert-molded lead frame 501 forms theoptical bottom surface of the optical element 109. Pre-attached to thelead frame 501 are the optical emitter 103 and the optical detector 104.The optical encoder device 500 does not comprise an optical lens,because the first surface 502 of the optical element 109 has athree-dimensional parabolic shape. Therefore, the first surface 502 actsas a total reflecting mirror as well as a collimator for lightencountering in light emission direction E from the light emitter 103.Thus, the light, which is totally reflected from the first surface 502,forms a parallel light beam before it encounters the second surface 111.As already mentioned above, the first surface 502 and/or the secondsurface 111 may be coated with reflective material to make the opticalelement 109 less susceptible to manufacturing inaccuracies of theoptical encoder device 500 or fluctuations of the light emissiondirection E during the operation of the light emitter 103 and, therebyto prevent an undesired light loss at the first surface 502 or thesecond surface 111, respectively.

[0037] According to the third preferred embodiment of the presentinvention, the second surface 111 encloses an angle of at leastsubstantially +45° with respect to the light emission direction E of thelight emitter 103. The light, which enters the optical element 109 abovethe optical emitter 103 and travels along the optical path 108,encounters the first surface 502, is totally reflected and collimated atthe first surface 502 and directed towards the second surface 111. Aftertraveling to the second surface 111, this light is totally reflected atthe second surface 111 such that it is now directed to the opticaldetector 104. Therefore, due to the first surface 502 and the secondsurface 111, the optical path 108 is substantially U-shaped. Accordingto the third preferred embodiment of the present invention and similarto the first preferred embodiment of the present invention, the freearea 113 is arranged inside the optical element 109 between the firstsurface 502 and the second surface 111.

[0038] The use of a three-dimensional parabolic shaped first surface 502instead of a collimating optical lens together with a flat first surfacehas the advantage that the parallelism of the light beam traveling alongthe residual optical path 108 is increased and, therefore, theperformance of the optical encoder device 500 is enhanced.

[0039]FIG. 6 shows a cross-section through an optical encoder device 600according to a fourth preferred embodiment of the present invention.Parts already known from FIG. 1, FIG. 4 or FIG. 5 will not be describedagain.

[0040] The only difference between the optical encoder device 600according to the fourth preferred embodiment of the present inventionand the optical encoder device 500 according to the third preferredembodiment of the present invention is that the free area 113 isarranged inside the optical element 109 between the second surface 111and the optical detector 104. The fact that the free area 113 ispositioned closer to the optical detector 104 has the advantages thatoptical diffractions caused by the optical encoding unit 112 arereduced, since the residual optical path 108 between the opticalencoding unit 112 and the optical detector 104 is short, and that theresponse time to a movement of the optical encoding unit 112 is reduced.

[0041] In the following table 1, the number and kind of piece partsneeded for manufacturing an optical encoder device is compared for theoptical encoder devices 500 and 600 according to the third and fourthpreferred embodiments of the present invention, for the optical encoderdevices 100 and 400 according to the first and second preferredembodiments of the present invention, as well as for the first andsecond optical encoder devices 301 and 310 according to the prior art.TABLE 1 first type of optical second type of optical optical encoderoptical encoder encoder device 301 encoder device 310 No. devices 500and 600 devices 100 and 400 (prior art) (prior art) 1 Substrate (insert-Substrate (lead Substrate (lead Substrate (lead molded lead frame)frame) 101 with frame) 302 with frame) 314 for optical 501 withelectrical electrical circuitry electrical circuitry emitter 208 withcircuitry 102 102 102 electrical circuitry (not shown) 2 optical emitter103 optical emitter 103 optical emitter 208 optical emitter 208 3optical detector 104 optical detector 104 optical detector 209 housingmaterial for optical emitter element 312 4 optical element 109 capsule105 for capsule 303 for Substrate (lead optical emitter 103 opticalemitter 208 frame) 314 for optical detector 209 with electricalcircuitry (not shown) 5 Wire capsule 105 for capsule 303 for opticaldetector 209 optical detector 104 optical detector 209 6 Die attach (DA)optical lens 107 housing material housing material for 304 opticaldetector element 313 8 Epoxy optical element 109 optical lens 210encoder housing 311 9 Wire window 305 optical lens 210 9 Epoxy mountingbracket Wire (not shown) 10 Wire Epoxy 11 Epoxy

[0042] From table 1 it becomes clear that the present invention,especially each of the third and fourth preferred embodiments, reducesthe number of needed piece parts for an optical encoder device.Therefore, an optical encoder device according to the present inventionconsiderably reduces the manufacturing processes as well as theproduction costs.

What is claimed is:
 1. An optical encoder device, comprising: an opticalemitter emitting light, the optical emitter having a light emissiondirection; an optical detector detecting light emitted by the opticalemitter, the optical detector having a light detection directiondifferent from the light emission direction; an optical elementcontrolling an optical path between the optical emitter and the opticaldetector such that light emitted by the optical emitter is detected bythe optical detector; and a free area in the optical encoder deviceaccommodating a moveable optical encoding unit comprising a plurality ofalternating transparent and opaque encoding elements wherein theplurality of alternating transparent and opaque encoding elements of theoptical encoding unit affects the optical path.
 2. The optical encoderdevice of claim 1 wherein the optical emitter and the optical detectorare arranged so that the light emission direction and the lightdetection direction are at least substantially antiparallel.
 3. Theoptical encoder device of claim 2 wherein the optical element isarranged so that the optical path is at least substantially U-shaped. 4.The optical encoder device of claim 3 wherein the optical elementprovides total internal reflection inside the optical element.
 5. Theoptical encoder device of claim 4 wherein the optical element comprisesa first surface and a second surface facing each other, the first andsecond surfaces reflecting light emitted by the optical emitter andcontrolling the optical path between the optical emitter and the opticaldetector.
 6. The optical encoder device of claim 5 wherein the first andsecond surfaces are flat, the first surface enclosing a first angle ofat least substantially −45° with respect to the light emissiondirection, and the second surface enclosing a second angle of at leastsubstantially +45° with respect to the light emission direction.
 7. Theoptical encoder device of claim 6 further comprising a lens next to theoptical emitter collimating light emitted by the optical emitter intoparallel light beams before it travels along the optical path.
 8. Theoptical encoder device of claim 5 wherein the first surface is parabolicand the second surface is flat, and the second surface enclosing anangle of at least substantially +45° with respect to the light emissiondirection, and the first surface is collimating light emitted by theoptical emitter into parallel light beams.
 9. The optical encoder deviceof claim 5 wherein the free area accommodating the optical encoding unitis accommodated in the optical element.
 10. The optical encoder deviceof claim 5 wherein the free area accommodating the optical encoding unitis arranged between the first and second surfaces.
 11. The opticalencoder device of claim 5 wherein the free area accommodating theoptical encoding unit is arranged between the second surface and theoptical detector.
 12. The optical encoder device of claim 5 wherein atleast one of the first and second surfaces is coated with reflectivematerial.
 13. The optical encoder device of claim 5 wherein the firstand second surfaces of the optical element reflect light emitted by theoptical emitter.
 14. The optical encoder device of claim 1 wherein theoptical encoding unit is a codewheel or a codestrip.
 15. The opticalencoder device of claim 1 further comprising a signal processorprocessing signals generated by the optical detector on the basis of amovement of the optical encoding unit affecting the optical path in thefree area.
 16. The optical encoder device of claim 1 wherein at leastone of the optical emitter and the optical detector is covered by acapsule.
 17. The optical encoder device of claim 1 wherein the opticalemitter and the optical detector are arranged on a substrate.
 18. Theoptical encoder device of claim 1 wherein the optical emitter is a lightemitting diode.
 19. The optical encoder device of claim 1 wherein theoptical detector comprises an array of photodiodes.
 20. The opticalencoder device of claim 1 wherein the optical element is integrallyformed.